Intraoperative Assessment of Intestinal Viability by Laser Doppler Flowmetry for Surgery of Ruptured Abdominal Aortic Aneurysms

Abstract

Ischemic colitis is a well known complication following surgery of ruptured abdominal aortic aneurysms, occurring in up to 60% of these patients. It is caused by failure to restore adequate blood flow to the watershed areas of the sigmoid colon. The purpose of this prospective study was to investigate erythrocyte flux to defined areas of the colon immediately after repair of ruptured abdominal aortic aneurysms using laser Doppler flowmetry (LDF) and to determine the critical level of erythrocyte flux below which revascularization of the colon is indicated. A group of 22 patients with a ruptured infrarenal aortic aneurysm in whom the inferior mesenteric artery was ligated at surgery were studied prospectively. Multiple LDF measurements of bowel blood flow (four per bowel segment) were performed on 103 intestinal segments intraoperatively using a Periflux 4001 Master with a PF 415:1 probe. In addition, histologic findings of ischemically injured intestine biopsied at routine postoperative endoscopy or postmortem examination were compared with the LDF records. There was a 41% incidence (9/22 patients) of postoperative colonic ischemia with a significant decrease in colonic erythrocyte flux below 50 perfusion units (PU) intraoperatively in all nine patients (100%). Four patients had transmural colon necrosis, and two patients died, for an overall mortality of 27%. Five patients were identified as having mild or moderate intestinal ischemia and were treated conservatively. Another 14 patients had no clinical or endoscopic signs of ischemic colitis. Erythrocyte flux in those colonic segments were > 50 PU. An intraoperative LDF recording of < 50 PU achieved a sensitivity of 100% (32/32 colon segments) and a positive prediction value of 100% in patients who developed ischemic colitis after surgery for ruptured abdominal aortic aneurysms. The results of this study demonstrate that LDF is a sensitive guide to and feasible method for evaluating critical colonic blood flow during repair of ruptured abdominal aortic aneurysm. The critical level of microvascular perfusion of the colon wall was found to be around 50 PU, below which revascularization of the colon should be considered to reduce the risk of subsequent ischemic colitis.